Implement AndroidWebViewController.setMixedContentMode

Author: daohoangson

packages/fwfh_webview/test/mock_webview_platform.dart

@@ -203,6 +203,10 @@ class __FakeAndroidWebViewController extends FakeWebViewController
     androidMediaPlaybackRequiresUserGesture = require;
   }
 
+  @override
+  Future<void> setMixedContentMode(MixedContentMode mode) =>
+      throw UnimplementedError();
+
   @override
   Future<void> setOnShowFileSelector(
     Future<List<String>> Function(FileSelectorParams params)?